WASHINGTON (CNN) -- The FBI sent agents to Guantanamo Bay in 2006 to independently obtain information the CIA had gotten from "high-value" al Qaeda detainees, but without using harsh interrogation techniques, a government official told CNN Tuesday.

More than 300 foreign nationals are being held at the U.S. Navy Base at Guantanamo Bay, Cuba.

The official asked not to be named because information about the questioning is classified.

FBI Director Robert Mueller had told agents to stay out of the CIA interrogations because of concern that the way the information was being obtained would not hold up in a court of law, the official said.

The CIA used harsh interrogation techniques, including waterboarding, during its questioning of three top al Qaeda detainees, CIA Director Michael Hayden said last week.

Waterboarding involves strapping a person to a surface, covering his face with cloth and pouring water on the face to imitate the sensation of drowning. Critics have called it torture.

There are questions about whether testimony gathered through waterboarding would be considered as testimony, said Charles Swift, a former U.S. Navy attorney who represented Osama bin Laden's driver.